What Is Alt Text?

Alt text (alternative text) is a written description of an image, added in the HTML, that describes what the image shows. It serves two main purposes: it lets screen readers describe images to visually impaired users, and it helps search engines understand image content. Good alt text is first about accessibility — and image SEO follows naturally from doing it well.

Here’s what alt text does, why accessibility comes first, and how to write it well.

What alt text does

Alt text is added via the alt attribute on an image in HTML. It works in a few situations:

• Screen readers read it aloud so visually impaired users know what an image shows.
• When an image fails to load, the alt text displays in its place.
• Search engines use it to understand image content, which supports image search and overall page context.

So alt text is where accessibility and SEO overlap: the same description that helps a screen reader also helps a search engine.

Accessibility comes first

Here’s the honest framing that keeps alt text useful: write it for accessibility first, and SEO takes care of itself. Its primary purpose is helping people who can’t see the image understand it. When you describe images genuinely and accurately for that reason, you naturally produce the clear, relevant descriptions search engines value too. Writing alt text purely to stuff keywords misses the point and produces worse descriptions for everyone.

How to write good alt text

• Describe the image accurately and specifically — “golden retriever catching a frisbee at a park,” not “dog.”
• Keep it concise — a phrase or short sentence, not a paragraph.
• Include a keyword only if it fits naturally — never force it.
• Don’t start with “image of” — screen readers already announce it’s an image.
• Skip alt text for purely decorative images — use an empty alt="" so screen readers ignore them.
• Include text that appears in the image if it’s meaningful.

Alt text and SEO

For SEO, good alt text helps your images rank in image search and adds relevant context to the page. It’s a modest signal, not a major ranking lever — so the payoff is real but proportionate. Treat it as part of thorough on-page SEO and good technical SEO hygiene: do it well on every meaningful image, don’t obsess, and never sacrifice a clear description to cram in a keyword. (SEO consulting covers this as part of the full on-page picture.)

Frequently asked questions

What is alt text in simple terms? Alt text (alternative text) is a written description of an image added in the HTML that describes what the image shows. It lets screen readers describe images to visually impaired users, displays if an image fails to load, and helps search engines understand image content. Its first purpose is accessibility, with image SEO following naturally.

Why is alt text important? It’s important primarily for accessibility — screen readers use it to describe images to visually impaired users, making your content usable for everyone. It also helps search engines understand your images, supporting image search and page context, and it displays if an image fails to load. It serves users and search engines at once.

How do I write good alt text? Describe the image accurately and specifically, keep it concise, and include a keyword only if it fits naturally. Avoid starting with “image of,” since screen readers already announce images. Use an empty alt attribute for purely decorative images so screen readers skip them, and include any meaningful text shown in the image.

Does alt text help SEO? Yes, modestly. Good alt text helps your images rank in image search and adds relevant context to the page, but it’s a minor signal rather than a major ranking factor. The bigger reason to write it well is accessibility — and doing that naturally produces the clear, relevant descriptions that also benefit SEO.

Should I put keywords in alt text? Only if they fit naturally and accurately describe the image. Alt text should describe the image for people who can’t see it, so forcing keywords produces worse descriptions and misses the point. Write an accurate, specific description first, and if your target keyword genuinely fits, include it — but never at the expense of clarity.

Do decorative images need alt text? No. Purely decorative images that add no information should have an empty alt attribute (alt="") so screen readers skip them rather than announcing meaningless descriptions. Reserve descriptive alt text for images that convey information. This keeps the experience clean for screen-reader users and focuses alt text where it actually matters.

What happens if I don’t add alt text? Without alt text, visually impaired users relying on screen readers can’t understand your images, which hurts accessibility and may raise compliance concerns. Search engines also lose context about the image, and nothing displays if the image fails to load. Adding accurate alt text to meaningful images avoids these gaps and improves the experience for everyone.

Written by Bryan Collins, SEO & AEO strategist. Want thorough, accessible on-page SEO? See SEO done for you or run a free local search audit.